1. Field of the Invention
The present invention relates to a light source device that includes a discharge tube with a discharge medium sealed therein and electrodes for exciting the discharge medium, and relates to a liquid crystal display employing the light source device.
2. Related Background Art
Recently, regarding backlights (light source devices) for use in liquid crystal displays, etc., earnest studies have been made on backlights in which mercury is not used (a backlight of this type hereinafter sometimes is referred to as mercuryless backlight), in addition to the studies on backlights in which mercury is used. The mercuryless backlight, which does not employ mercury, does not suffer from a decrease in a light emission efficiency caused by a rise of mercury temperature, thereby having an advantage of quicker start of the emission of luminous fluxes. Further, the mercuryless backlight is environmentally preferable.
As a light source device in which mercury is not used, a discharge lamp device is disclosed that includes a bulb in which a rare gas is sealed, an inner electrode provided inside the bulb, and an outer electrode provided outside the bulb (JP 5-29085 A). The outer electrode is a linear electrode, and is formed on an outer surface of the bulb so as to be parallel with a central axis of the bulb. By applying a voltage across the inner and outer electrodes, this rare gas discharge lamp device emits light.
Further, a rare gas discharge lamp is disclosed that includes a discharge tube in which a rare gas is sealed, an inner electrode formed inside the discharge tube, and an outer electrode formed spirally on an outer surface of the discharge tube (JP 10-112290 A).
Furthermore, as a discharge lamp with a rare gas as a principal discharge medium, a discharge lamp is disclosed that includes an air-tight vessel, an inner electrode provided inside the air-tight vessel, and an outer electrode in such a form as a coil form, a mesh form, etc. (JP 2001-325919 A). This gazette discloses a method of fixing the outer electrode using a shrinkable tube.
Furthermore, a discharge lamp disclosed in U.S. Pat. No. 5,604,410 includes a discharge tube in which a rare gas is sealed, an inner electrode, and an outer electrode. The inner electrode is formed along a central axis of the discharge tube throughout a substantial entirety of the discharge tube. The outer electrode is a linear electrode, and is formed on an outer surface of the discharge tube so as to be parallel with a central axis of the discharge tube.
However, in the case where a linear outer electrode is formed throughout a substantial entirety of the discharge tube, the discharge is concentrated in the vicinity of the outer electrode, thereby becoming constricted. This sometimes makes it impossible to excite the discharge medium efficiently, sometimes resulting in a decrease in the light emission efficiency. In the case where an outer electrode in a spiral form is provided on an outer surface of a discharge tube, the discharge also tends to be constricted, since the outer electrode is brought into contact linearly with the outer surface of the discharge tube.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a novel light source device, and a liquid crystal display device employing the same.
To achieve the foregoing object, a light source device of the present invention includes at least one discharge tube, a discharge medium sealed inside the discharge tube, and first and second electrodes for exciting the discharge medium. The first electrode is formed inside or outside the discharge tube, and the second electrode is in contact with an outer surface of the discharge tube at a plurality of contact portions, the contact portions being located at different distances from the first electrode and being provided discontinuously. It should be noted that cases in which the xe2x80x9ccontact of the second electrode with the outer surface of the discharge tubexe2x80x9d is achieved include a case where the second electrode and the discharge tube are in contact with each other via a dielectric or the like. The xe2x80x9ccontactxe2x80x9d between two members herein means that no air space is present therebetween.
In the foregoing light source device, the plurality of the contact portions may be arranged in a tube axial direction of the discharge tube.
In the foregoing light source device, the first electrode may be formed at an end of the discharge tube, and a surface density of the plurality of the contact portions may increase with decreasing proximity to the first electrode.
In the foregoing light source device, a surface of the first electrode may be covered with a dielectric.
The foregoing light source device may further include a phosphor layer formed on an inner surface of the discharge tube.
In the foregoing light source device, the discharge tube may include a glass tube, and a dielectric layer formed on an outer surface of the glass tube.
In the foregoing light source device, the second electrode may be in contact with the discharge tube via a dielectric.
In the foregoing light source device, the discharge medium may contain xenon gas, and further may contain mercury. Alternatively, in the foregoing light source device, the discharge medium containing no mercury is applicable.
The foregoing light source device further may include a supporting plate, and the discharge tube may be arranged on a side of the supporting plate.
In the foregoing light source device, the supporting plate may receive light emitted from the discharge tube and radiate the same from one principal surface of the supporting plate.
The foregoing light source device further may include a supporting plate, and may be configured so that a plurality of the discharge tubes are held on the supporting plate, the second electrode includes a plurality of linear electrodes arranged in parallel, and the discharge tubes are arranged so as to be perpendicular to the linear electrodes.
In the foregoing light source device, the discharge tubes may include a plurality of first discharge tubes, a plurality of second discharge tubes, and a plurality of third discharge tubes. The first, second, and third discharge tubes are arranged in the stated order repetitively, and the first, second, and third discharge tubes emit lights with wavelengths different from each other, respectively.
The foregoing light source device further may include a third electrode arranged on an inner surface of or around the discharge tube. The third electrode is formed in a linear form so as to be arranged in parallel with a tube axis of the discharge tube, and a potential E1 of the first electrode, a potential E2 of the second electrode, and a potential E3 of the third electrode satisfy relationships expressed as |E2|xe2x89xa6E3| less than |E1| and 0xe2x89xa6E1xc2x7E3.
In the foregoing light source device, both ends of the third electrode may be connected with the second electrode at two contact portions selected from the plurality of the contact portions.
A liquid crystal display of the present invention includes the above-described light source device of the present invention, and a liquid crystal panel that transmits light emitted from the light source device. The light source device includes at least one discharge tube, a discharge medium sealed inside the discharge tube, and first and second electrodes for exciting the discharge medium. In the light source device, the first electrode is formed inside or outside the discharge tube, and the second electrode is in contact with an outer surface of the discharge tube at a plurality of contact portions, the contact portions being located at different distances from the first electrode and being provided discontinuously.
The light source device in the liquid crystal display further may include a light-guiding plate that receives light emitted from the discharge tube and allows the light to leave a principal surface thereof. The liquid crystal panel is arranged so as to face the light-guiding plate.
Furthermore, the light source device in the liquid crystal display may further include a supporting plate, and may be configured so that a plurality of the discharge tubes are held on the supporting plate, the second electrode includes a plurality of linear electrodes arranged in parallel, and the discharge tubes are arranged so as to be perpendicular to the linear electrodes.